This invention deals generally with the use of ultraviolet radiation to sterilize liquids and more specifically with an apparatus and method to kill bacteria in a fluid which is essentially opaque to ultraviolet radiation.
The exposure of liquids to ultraviolet radiation in order to sterilize them by killing bacteria is a long established technique. Many patents have been issued which are based on the ability of ultraviolet radiation to destroy bacteria, and such devices are common enough to be in use in many households and industries. Typically, such systems expose water to ultraviolet radiation by passing the water through an enclosure in which it is exposed to ultraviolet radiation. In some such devices the water is routed around a cylindrical lamp by directing it a spiral path, thus increasing the time during which the water is exposed to radiation, and assuring a more complete kill of the bacteria within the water.
One consideration which pervades all the prior art and is so well accepted that it is rarely even mentioned is that the treatment of water by exposure to ultraviolet radiation depends upon the water itself being significantly transparent to the ultraviolet radiation. The penetration of ultraviolet radiation through water typically may range from a few inches to more than a foot. Without such transparency to ultraviolet radiation, the purification of the water is very difficult because only the surface of the water in actual contact with the source of radiation is affected by the ultraviolet radiation. In fact, several patents on the subject suggest prefiltering the water to remove particles before treating it with ultraviolet radiation.
However, there are some applications in which it is required that fluids which are opaque to ultraviolet radiation be treated to kill bacteria. One such application is for the treatment of industrial cooling fluids such as oil and water emulsions in which bacteria must be destroyed to prevent threats to human health, deterioration of the coolant fluid, and the generation of noxious odors.
Another application which is more familiar to most people, and for which ultraviolet radiation has not been generally used, is the treatment of sewage. In both of these applications the fluid is essentially opaque and the use of ultraviolet radiation has been given little consideration. The accepted treatment for such applications has been the use of chemical biocides to inhibit the growth of or destroy bacteria. Unfortunately, the use of chemical biocides presents other problems. While the chemical biocides have been generally successful in destroying bacteria, they are also dangerous to humans and other animal life. Chemical biocides therefore pose a hazard in the industrial environment and create a significant problem in regard to disposal at the end of the useful life of the fluids with which they are used.
Therefore, it would highly desirable to have available a device which can use ultraviolet radiation to kill bacteria in fluids which are essentially opaque to ultraviolet radiation.